The above mentioned types of footwear generally comprise a sole assembly, formed at least by an outsole or bottom and an insole or foot bed, and an open upper, made of leather, fabric, plastic or any other flexible material. The upper may be formed by one or more straps, some of them of adjustable length, to encircle the user's foot, such as in a sandal, or by a band transversally extending from one side to the other of the sole such as in clogs and slippers. The upper is in any case fixedly connected to the sole generally by means of gluing, screws or nails.
Due to this type of connection, which is irreversible or, anyway, hardly disassemblable by means of suitable tools only, and also for aesthetical reasons related to the color or the shape of the upper, a footwear of the above mentioned type is generally purchased to be worn in combination with a well defined type of clothing or even with a specific cloth. As a result, the possibility of use of a single pair of sandals or clogs may be relatively limited and several pairs of them are needed to match each different cloth.